Windows on buildings and houses provide light into rooms and good view to the outside. However, heat from the sun easily enters and exits through windows, causing excess heating in the summer and constant heat loss in the winter. Also, sunlight causes glare and furniture fading inside rooms. For these problems, blinds or shutters are the common solution; however, they block outside view, which defeats the purpose of windows. Blinds and shutters also darken the room motivating people to turn on lights, increasing energy consumption.
To reduce this high energy consumption, different solutions exist, though most (if not all) are affected by the teeter-totter effect: energy savings in winter result in energy losses in summer, and vice versa. Some of these technologies inhibit the green house effect such as low-E (low-emissivity) glass where a surface of the Insulated Glass Unit (IGU) has an Infra-Red (IR) reflecting layer, typically in the form of silver metal coating. This technology reflects IR and some VIS (visible light), and keeps heat on the outside of buildings. However, low-E windows do not vary with the seasons and can not be applied to existing windows.
Other existing technologies used to reduce the energy consumption of buildings are based on electrochromic windows, such as those sold by Sage Glass. In the Sage electrochromic window, electric voltage is applied to darken the glass and block VIS and IR in the summer Like low-E, electrochromic glass can not be applied to existing windows. In addition, electrochromic windows are extremely expensive costing over $1,000 per window, and require electricity (more energy) to operate.
Another fenestration technology used to save energy is the tinted or mirrored window film. Those films are usually applied to windows to reduce glare and brightness of the sun and to reflect IR wavelengths, thereby reducing solar heat gain in the room as described in US2006/0154049 and U.S. Pat. No. 7,057,805. This solution can save on cooling costs in hot climates and is perfect for subtropical cities. However, window films reject solar radiation year-round, meaning colder climates lose valuable solar heating in winter, increasing heating costs for the building.
Novel window designs were proposed by Franz (U.S. Pat. No. 4,081,934), Gell (U.S. Pat. No. 4,180,954), and Gillery (U.S. Pat. No. 4,235,048) where an IR reflecting coating is applied to one surface of a sheet of glass and the window is rotated in its frame when the seasons change. This results in the IR reflecting coating facing outside in the summer, minimizing solar heat gain, and facing the inside of the room in the winter months reflecting IR back into the room. A different solution was proposed by Bliamptis (U.S. Pat. No. 4,365,620) where a reversible double pane window with one pane adapted to block IR radiation is described. The entire window is adapted to pivot about a horizontal axis allowing for solar heating in winter and cooling in the summer Erell (US2006/0225353) proposes a rotatable window pane assembly that provides year-round energy savings but requires moving a “solar energy absorbing” glass pane from the interior to the exterior of a building by rotating the window pane. Also, the proposed window pane assembly requires complex window design, can not be applied to existing windows, and exposes the absorbing glass pane to the harsh exterior elements.
Therefore, there exists a need for a year-round energy saving solution for windows where such a solution can be applied to both existing windows and new windows, and does not require rotation of the window in its frame.